[clang] Ensure -mno-outline adds attributes #163692
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This was referenced Oct 16, 2025
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@llvm/pr-subscribers-clang-codegen @llvm/pr-subscribers-clang-driver Author: Sam Elliott (lenary) ChangesBefore this change, The drawback of this implementation is that, when using LTO, only the This change serialises the Full diff: https://github.com/llvm/llvm-project/pull/163692.diff 9 Files Affected:
diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
index 90e1f8d1eb5e9..4ccb75ebf904b 100644
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -489,6 +489,9 @@ CODEGENOPT(ResMayAlias, 1, 0, Benign)
ENUM_CODEGENOPT(WinX64EHUnwindV2, WinX64EHUnwindV2Mode,
2, WinX64EHUnwindV2Mode::Disabled, Benign)
+/// Adds attributes that prevent outlining (`-mno-outline`)
+CODEGENOPT(DisableOutlining, 1, 0, Benign)
+
/// FIXME: Make DebugOptions its own top-level .def file.
#include "DebugOptions.def"
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d62b771f463ea..729be4f09c034 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -5127,16 +5127,13 @@ def mms_bitfields : Flag<["-"], "mms-bitfields">, Group<m_Group>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Set the default structure layout to be compatible with the Microsoft compiler standard">,
MarshallingInfoFlag<LangOpts<"MSBitfields">>;
-def moutline
- : Flag<["-"], "moutline">,
- Group<f_clang_Group>,
- Visibility<[ClangOption, CC1Option]>,
- HelpText<"Enable function outlining (AArch64,Arm,RISC-V,X86 only)">;
-def mno_outline
- : Flag<["-"], "mno-outline">,
- Group<f_clang_Group>,
- Visibility<[ClangOption, CC1Option]>,
- HelpText<"Disable function outlining (AArch64,Arm,RISC-V,X86 only)">;
+defm outline
+ : BoolMOption<
+ "outline", CodeGenOpts<"DisableOutlining">, DefaultFalse,
+ NegFlag<SetTrue, [], [ClangOption, CC1Option],
+ "Disable function outlining (AArch64,Arm,RISC-V,X86 only)">,
+ PosFlag<SetFalse, [], [ClangOption],
+ "Enable function outlining (AArch64,Arm,RISC-V,X86 only)">>;
def mno_ms_bitfields : Flag<["-"], "mno-ms-bitfields">, Group<m_Group>,
HelpText<"Do not set the default structure layout to be compatible with the Microsoft compiler standard">;
def mskip_rax_setup : Flag<["-"], "mskip-rax-setup">, Group<m_Group>,
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ab267236ed579..ca3ef780d2853 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2820,7 +2820,9 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
B.addAttribute(llvm::Attribute::MinSize);
}
- if (D->hasAttr<NoOutlineAttr>())
+ // Add `nooutline` if Outlining is disabled with a command-line flag or a
+ // function attribute.
+ if (CodeGenOpts.DisableOutlining || D->hasAttr<NoOutlineAttr>())
B.addAttribute(llvm::Attribute::NoOutline);
F->addFnAttrs(B);
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 24b12fbf88f6f..a03b34ffb5d50 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -2923,13 +2923,16 @@ void tools::addMachineOutlinerArgs(const Driver &D,
Triple.isRISCV() || Triple.isX86())) {
D.Diag(diag::warn_drv_moutline_unsupported_opt) << Triple.getArchName();
} else {
- // FIXME: This should probably use the `nooutline` attribute rather than
- // tweaking Pipeline Pass flags, so `-mno-outline` and `-moutline`
- // objects can be combined correctly during LTO.
+ // Enable Pass in pipeline
addArg(Twine("-enable-machine-outliner"));
}
} else {
- // Disable all outlining behaviour.
+ if (!IsLTO)
+ // Disable all outlining behaviour using `nooutline` option, in case
+ // Linker Invocation lacks `-mno-outline`.
+ CmdArgs.push_back("-mno-outline");
+
+ // Disable Pass in Pipeline
addArg(Twine("-enable-machine-outliner=never"));
}
}
diff --git a/clang/test/CodeGen/attr-nooutline.c b/clang/test/CodeGen/attr-nooutline.c
index b9f175da24cb5..ed3565b7f1166 100644
--- a/clang/test/CodeGen/attr-nooutline.c
+++ b/clang/test/CodeGen/attr-nooutline.c
@@ -1,6 +1,7 @@
// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --check-attributes --version 6
-// RUN: %clang_cc1 -emit-llvm %s -triple x86_64-unknown-linux-gnu -disable-O0-optnone -o - | FileCheck %s
-
+// RUN: %clang_cc1 -emit-llvm %s -triple x86_64-unknown-linux-gnu -disable-O0-optnone -DATTR -o - | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm %s -triple x86_64-unknown-linux-gnu -disable-O0-optnone -mno-outline -o - | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm %s -triple x86_64-unknown-linux-gnu -disable-O0-optnone -mno-outline -DATTR -o - | FileCheck %s
// CHECK: Function Attrs: noinline nooutline nounwind
// CHECK-LABEL: define dso_local i32 @t1(
@@ -11,6 +12,9 @@
// CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[X_ADDR]], align 4
// CHECK-NEXT: ret i32 [[TMP0]]
//
-[[clang::nooutline]] int t1(int x) {
+#ifdef ATTR
+[[clang::nooutline]]
+#endif
+int t1(int x) {
return x;
}
diff --git a/clang/test/Driver/aarch64-outliner.c b/clang/test/Driver/aarch64-outliner.c
index 5ed822f122fc4..4d5b7321e330f 100644
--- a/clang/test/Driver/aarch64-outliner.c
+++ b/clang/test/Driver/aarch64-outliner.c
@@ -3,4 +3,4 @@
// ON: "-mllvm" "-enable-machine-outliner"
// RUN: %clang --target=aarch64 -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
// RUN: %clang --target=aarch64_be -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
-// OFF: "-mllvm" "-enable-machine-outliner=never"
+// OFF: "-mno-outline" "-mllvm" "-enable-machine-outliner=never"
diff --git a/clang/test/Driver/arm-machine-outliner.c b/clang/test/Driver/arm-machine-outliner.c
index a1e705cb60a1b..efa29d2ab8450 100644
--- a/clang/test/Driver/arm-machine-outliner.c
+++ b/clang/test/Driver/arm-machine-outliner.c
@@ -3,6 +3,6 @@
// RUN: %clang -target armv7-linux-gnueabihf -flto -moutline %s -### 2>&1 | FileCheck %s -check-prefix=ON-LTO
// ON-LTO: "-plugin-opt=-enable-machine-outliner"
// RUN: %clang -target armv7-linux-gnueabihf -moutline -mno-outline -c %s -### 2>&1 | FileCheck %s -check-prefix=OFF
-// OFF: "-mllvm" "-enable-machine-outliner=never"
+// OFF: "-mno-outline" "-mllvm" "-enable-machine-outliner=never"
// RUN: %clang -target armv7-linux-gnueabihf -flto -moutline -mno-outline %s -### 2>&1 | FileCheck %s -check-prefix=OFF-LTO
// OFF-LTO: "-plugin-opt=-enable-machine-outliner=never"
diff --git a/clang/test/Driver/riscv-outliner.c b/clang/test/Driver/riscv-outliner.c
index 9e9905ab4fd8a..fa69977331e13 100644
--- a/clang/test/Driver/riscv-outliner.c
+++ b/clang/test/Driver/riscv-outliner.c
@@ -4,4 +4,4 @@
// RUN: %clang --target=riscv32 -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
// RUN: %clang --target=riscv64 -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
-// OFF: "-mllvm" "-enable-machine-outliner=never"
+// OFF: "-mno-outline" "-mllvm" "-enable-machine-outliner=never"
diff --git a/clang/test/Driver/x86-outliner.c b/clang/test/Driver/x86-outliner.c
index e2af85d3d16ab..7da56ac93fa5e 100644
--- a/clang/test/Driver/x86-outliner.c
+++ b/clang/test/Driver/x86-outliner.c
@@ -4,4 +4,4 @@
// RUN: %clang --target=i386 -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
// RUN: %clang --target=x86_64 -moutline -mno-outline -S %s -### 2>&1 | FileCheck %s -check-prefix=OFF
-// OFF: "-mllvm" "-enable-machine-outliner=never"
+// OFF: "-mno-outline" "-mllvm" "-enable-machine-outliner=never"
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Before this change, `-mno-outline` and `-moutline` only controlled the pass pipelines for the invoked compiler/linker. The drawback of this implementation is that, when using LTO, only the flag provided to the linker invocation is honoured (and any files which individually use `-mno-outline` will have that flag ignored). This change serialises the `-mno-outline` flag into each function's IR/Bitcode, so that we can correctly disable outlining from functions in files which disabled outlining, without affecting outlining choices for functions from other files. This matches how other optimisation flags are handled so the IR/Bitcode can be correctly merged during LTO.
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Before this change,
-mno-outlineand-moutlineonly controlled thepass pipelines for the invoked compiler/linker.
The drawback of this implementation is that, when using LTO, only the
flag provided to the linker invocation is honoured (and any files which
individually use
-mno-outlinewill have that flag ignored).This change serialises the
-mno-outlineflag into each function'sIR/Bitcode, so that we can correctly disable outlining from functions in
files which disabled outlining, without affecting outlining choices for
functions from other files. This matches how other optimisation flags
are handled so the IR/Bitcode can be correctly merged during LTO.